The present invention relates to fluid-filled spherical shell generation and, more particularly, is concerned with multi-element spherical shell generation.
Fluid-filled spherical shells of material have been produced based on the phenomena of liquid jet flow instability and breakup. Materials which have been used for forming the shells include glasses, met-glasses, metals and plastics. Typical shell forming apparatuses are disclosed in U.S. Pat. Nos. to Mabbs (2,333,433 and 2,379,817) Frosch et al (4,279,632), Morishita et al (4,422,985 and 4,481,157), Kendall et al (4,643,854) and Wang et al (4,645,442).
For producing shells of 750 micrometer and greater diameter, one technique commonly employed is disclosed in U.S. Pat. No. 4,643,854 to Kendall et al cited above. The technique consists of pushing or forcing a stream of molten shell material, such as by gravity flow, through an outer one of a pair of concentric annular passages of a nozzle while flowing a continuous stream of a pressurized filler fluid, gas or liquid, through an inner one of the nozzle passages. When the velocities of concentric flows are in the proper range of values, a hollow jet instability occurs causing pinch-off of the jet, encapsulation of the filler fluid, and, due to surface tension, the formation of spherical shells.
Spherical shells of 750 micrometer or more in diameter are successfully produced in the apparatus of the Kendall et al patent by employing a filler material supply tube which extends through the shell material reservoir to the outlet nozzle and from which discrete bubbles of filler fluid are pushed into and entrained in the existing stream of molten shell material. The bubbles cause the fluid jet to form nodes and subsequently to break-up into shells due to the classical Rayleigh-Taylor instability phenomenon.
Solidification of the spherical shells is brought about typically by freezing of the molten shell material as the shells fall through a conventional cooling arrangement. Depending upon the material system selected, solidification can also occur by using alternative techniques, for example, by using a chemical process. The final shape of the solid spherical shell is a result of centering forces, surface tension, and aerodynamical and gravitational forces acting on the falling bubble and on its cooling rate. The reproducibility and precision of the product is frequently within a few percent.
Notwithstanding the overall effectiveness and success of the above-described technique in forming fluid-filled spherical shells, a need exists for improvement thereof so as to allow more versatility in the encapsulated and encapsulating materials composing the fluid-filled shells.